1. Field Of The Invention
The present invention relates generally to a device controller, and more particularly relates to a control circuit for variably controlling power to an appliance such as a heater, a humidifier and/or a fan.
2. Description Of The Prior Art
It is known in the art to control the velocity of a fan or power to a heater in response to changes in temperature and/or humidity. Generally, in a temperature control circuit, a transducer senses changes in temperature and a control circuit adjusts the power to a fan or power to a heater in response to the temperature changes. a humidifier control circuit generally has a humidity sensor and a control circuit that responds to changes in humidity by controlling the flow of air over a wick filter or by controlling the temperature of an evaporative water tank. The temperature and humidity control circuits typically include a triac which is used to control the AC power to the fan or heater.
Traditional control circuits consist of numerous discrete components. The use of discrete components tends to provide temperature and/or humidity control which is less accurate and less reliable. The poor accuracy is due to changing part tolerances and due to limitations within the discrete component circuit design.
Modem control circuits often include microcomputer type devices such as a microprocessor, a microcontroller or a digital signal processor. These control circuits typically result in improved accuracy and speed, but tend to be more costly. They involve numerous support logic such as address decode devices, memory devices and analog to digital converters, which increase the cost of the control circuitry. It would therefore be advantageous to have a sophisticated means for quickly and accurately adjusting fan velocity or heater power at a cost substantially less than that of the typical modern control circuit. It would also be advantageous to have a sophisticated means for adjusting fan velocity or power to a heating element that comprises substantially fewer components than that of the typical modern control circuits.
Conventional control circuits also react to changes in temperature and/or humidity by either switching the appliance On and Off or by switching between fixed appliance speeds, such as High and Low. This results in the actual temperature and/or humidity overshooting and/or undershooting the desired level. It would therefore be advantageous to have a control circuit that could variably control power to an appliance based on continuous monitoring and evaluation of the input parameter.
Thus, the present invention is directed toward overcoming the disadvantages of conventional temperature control circuits which have been discussed above.